The purpose of this study is to morphologically identify the mechanism by which lysosomal enzymes are secreted and taken up by human fibroblasts. Ultrastructural cytochemistry has been used to identify two populations of lysosomes. These populations have been found to be constant but one population disappears with mitosis and lysosomatropic drugs. The mechanism of this dispersal will be studied. Purification of the lysosomal enzyme arylsulfatase A will be attempted in addition to tracing its path of uptake by cytochemical methods.